1. Field of the Invention
This invention relates to an electrically heatable catalytic converter which is used for converting pollutant materials produced by an engine, for example, carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides etc., to carbon dioxide, nitrogen and water.
2. Description of Prior Art
An electrically heatable catalytic converter having a cylindrical catalytic core comprising a thin metal strip (usually consisting of a corrugated strip and a plane strip), and an insulation layer superimposed and spirally wound together, a cylindrical metal case for accommodating therein said catalytic core, and an electric source supplying means for electrically heating said metal strip, has been conventionally known in the prior art, such as disclosed in U.S. Pat. No. 5,070,694.
Japanese Unexamined Patent Publication (Kohyo) NO. 3-500911 discloses such a catalytic converter, in which the insulation layer extends to the outer periphery of the cylindrical catalytic core which is secured to the inner surface of the metal case.
To meet the recent requirements for the severe control of exhaust gas, HC and CO must be reduced during the engine starting condition. Thus, the catalytic core must rapidly be heated to the catalytic activation temperature.
In the known electrically heatable catalytic converter, however, since the insulation layer extends all over the catalytic core, i.e., the insulation layer exists in the entire region of the catalytic core. For example, if a relatively small volume of 100 cc must be heated up to 400.degree. C. in 10 sec., a large electric power, such as more than 2-3 kW, is necessary. Therefore, a larger power supply system including an existing battery is required. Thus, new problems on weight, cost, fuel consumption and so forth will arise.